The present invention relates to an ink cartridge for an ink-jet recording device, and more particularly, to an ink cartridge having a plurality of ink bags therein.
Generally, an ink-jet recording device is arranged such that an appropriate negative pressure (a pressure lower than atmosphere pressure) is created within an ink-jet printhead in order to maintain an ink meniscus formed in the ink-jet printhead. For example, if ink is supplied to the printhead from an ink bag provided within an ink cartridge, the ink bag is placed lower than the printhead to create negative pressure within the printhead by means of hydraulic head difference. In such an arrangement, however, the liquid level within the ink bag comes lower as the ink is consumed, resulting in change of the hydraulic head difference. Therefore, the dimension of the ink bag in the vertical direction has been limited, not only from reasons arising from the design of the ink-jet recording device, but also to keep the change of the hydraulic head difference within a predetermine range.
Recently, long size printheads, which are provided with a plurality of ink ejecting orifices arranged in the width direction of the recording medium, are widely used in order to increase the recording rate. Long size printheads, however, require large capacity ink bags since they consume large quantities of ink.
Japanese Patent Application Provisional Publication HEI 11-105299 discloses an ink-jet printer that has a flexible sub-tank provided on an ink channel connecting a printhead and a large capacity ink cartridge. A negative pressure is imparted to the printhead by means of hydraulic head difference between the sub-tank and the printhead. The printer provided with the sub-tank can keep the change of the hydraulic head difference caused by the consumption of the ink within a predetermined range while being capable of supplying sufficient amount of ink to the long size printhead from the large capacity ink cartridge.
However, the introduction of the sub-tank into the ink-jet printer requires a complicated ink channel structure and also increases the number of channel joints. Such ink channels may hardly allow bubbles to be discharged therefrom and/or have low ability of sealing gas and water vapor. Further, the flexible sub-tank should be frequently exchanged due to the low durability thereof.
In order to resolve the above-mentioned problem, it is suggested to replace the ink cartridge and the sub-tank with upper and lower ink bags directly connected to each other so that the complex ink channel connecting the ink cartridge and the sub-tank can be eliminated.
In the above case, the upper ink bag and lower ink bag serve as the ink cartridge and the sub-tank, respectively, and the ink flows from the upper ink bag into the lower ink bag due to its own weight. Thus, the consumed ink can be supplied into the lower ink bag (sub-tank bag) from the upper ink bag (the ink cartridge bag) without significant delay as long as the ink cartridge bag contains a large amount of ink. However, time required for supplying ink into the sub-tank bag increases as the amount of ink remaining in the ink cartridge bag decreases. This is because the weight of the ink within the ink cartridge bag decreases and also since the pressure within the ink cartridge bag becomes negative (lower than the atmosphere pressure). Although the printhead has the ability of high speed printing, the increase of the time required for replenishing the sub-tank bag with ink results in increase of the total printing time since the ink-jet recording device have to stop printing during the ink replenishment of the sub-tank bag. In addition, because of the negative pressure in the ink cartridge bag, not all of the ink therein can be consumed, but a small amount will be left.
Therefore, there is a need for an ink cartridge for an ink-jet recording device that is capable of implying negative pressure to the printhead without requiring a sub-tank to be provided within the ink-jet recording device, while being also capable of smoothly supplying a large amount of ink to the printhead irrespective of the ink amount remaining in the ink cartridge.